For typing in tables, you can use Text mode's definition of TAB,
tab-to-tab-stop. This command inserts indentation before point,
enough to reach the next tab stop column. If you are not in Text mode,
this command can be found on the key M-i.

You can specify the tab stops used by M-i. They are stored in a
variable called tab-stop-list, as a list of column-numbers in
increasing order.

The convenient way to set the tab stops is with M-x
edit-tab-stops, which creates and selects a buffer containing a
description of the tab stop settings. You can edit this buffer to
specify different tab stops, and then type C-c C-c to make those
new tab stops take effect. edit-tab-stops records which buffer
was current when you invoked it, and stores the tab stops back in that
buffer; normally all buffers share the same tab stops and changing them
in one buffer affects all, but if you happen to make
tab-stop-list local in one buffer then edit-tab-stops in
that buffer will edit the local settings.

Here is what the text representing the tab stops looks like for ordinary
tab stops every eight columns.